Variable valve timing apparatus for internal combustion engine

ABSTRACT

A variable valve timing apparatus includes a variable valve timing mechanism that includes a first rotating body and a second rotating body that are rotating bodies that rotate about the same rotational axis; advance chambers and retard chambers that serve as hydraulic pressure chambers into which hydraulic fluid is supplied from an oil pump; and a discharge passage that discharges hydraulic fluid from the hydraulic pressure chambers. At least one of the hydraulic pressure chambers that is communicated with the discharge passage in a position vertically higher than the rotational axis when the first rotating body and the second rotating body have stopped rotating at a given phase, and from which hydraulic fluid is discharged into the discharge passage, is placed in a state constantly open to ambient air regardless of the phase at which the first rotating body and the second rotating body have stopped.

INCORPORATION BY REFERENCE

The disclosure of Japanese Patent Application No. 2010-048139 filed on Mar. 4, 2010, including the specification, drawings and abstract is incorporated herein by reference in its entirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to a variable valve timing apparatus for an internal combustion engine, that is provided with a variable valve timing mechanism that changes the valve timing of an intake valve and an exhaust valve, a lock mechanism that fixes the valve timing at an intermediate angle between a most retarded angle and a most advanced angle, and a discharge passage that extends from an advance chamber and a retard chamber to a rotational axis side of a camshaft and that enables hydraulic fluid to be discharged from each chamber.

2. Description of the Related Art

One variable valve timing apparatus for an internal combustion engine that has been put into practical use rotates a first rotating body that is drivingly connected to a crankshaft and a second rotating body that is drivingly connected to a camshaft relative to each other using the hydraulic pressure of hydraulic fluid supplied from an oil pump, and changes the valve timing of an intake valve and an exhaust valve that are opened and closed by the camshaft, by changing the relative rotation phase of the camshaft with respect to the crankshaft.

Hereinafter, an example structure of a variable valve timing apparatus, including that of the related art, will be described with reference to FIG. 11. Incidentally, in FIG. 11, reference character “R” indicates the rotational direction of a camshaft, not shown, and reference character “C” indicates the rotational axis of the camshaft. A plurality of concave portions 301 are provided surrounding the rotational axis of the camshaft in a first rotating body 300, while a plurality of vanes 401 that extend in the radial direction of the rotational axis of a second rotating body 400 and that are arranged inside the concave portions 301 are provided on the second rotating body 400. Also, the insides of the concave portions 301 are divided by the plurality of vanes 401. An advance chamber 510 and a retard chamber 520 are formed sandwiching each of the vanes 401.

Also, an advance oil passage 610 and a retard oil passage 620 that are communicated with the advance chamber 510 and the retard chamber 520 and supply and discharge hydraulic fluid to and from the oil chambers 510 and 520, respectively, are both formed mainly by an axial passage, not shown, and a radial passage 611 and 621. The axial passage extends along in the axial direction inside the camshaft. The radial passages 611 and 621 are connected to the axial passage at an end portion of the camshaft and extend in the radial direction, and are connected to the advance chamber 510 and the retard chamber 520. Also, when the valve timing is advanced, for example, hydraulic fluid is supplied from the oil pump to the advance chamber 510 through the axial passage and the radial passage of the advance oil passage 610, and hydraulic fluid in the retard chamber 520 is returned to an oil pan through the axial passage and the radial passage of the retard oil passage 620.

On the other hand, when the valve timing is retarded, hydraulic fluid is supplied from the oil pump to the retard chamber 520 through the radial passage and the axial passage of the retard oil passage 620, and hydraulic fluid in the advance chamber 510 is returned to the oil pan through the radial passage and the axial passage of the advance oil passage 610. Further, the supply and discharge of hydraulic fluid to and from the oil chambers 510 and 520 in this way is controlled via a flow control valve 700 provided midway in the advance oil passage 610 and the retard oil passage 620.

Also, another known variable valve timing apparatus is provided with a lock mechanism 800 that fixes the valve timing at a predetermined intermediate angle by fixing the relative rotation phase of both rotating bodies 300 and 400 at an intermediate phase that excludes a most retarded phase and a most advanced phase in a region in which the rotating bodies 300 and 400 are able to rotate relative to one another. Incidentally, this intermediate angle is set to an angle that is most appropriate when starting the engine, for example. As a result, good engine startability can be ensured.

Also, one representative example of such a lock mechanism 800 is a lock mechanism that mechanically restricts relative rotation of the rotating bodies by having a lock pin 801 protrude out from one rotating body, from among the two rotating bodies 300 and 400, toward the other rotating body, and engaging this lock pin 801 with a lock hole 802 formed in the other rotating body.

More specifically, a housing space, not shown, is formed in the one rotating body and the lock pin 801 that is urged by the elastic force of a spring, not shown, is housed in this housing space. Also, a release chamber, not shown, is formed in a portion of the housing space. When hydraulic fluid is supplied to this release chamber, the force generated by the hydraulic pressure urges the lock pin 801 in the direction opposite the urging direction of the spring against the urging force of the spring. Also, the lock hole 802 with which the lock pin 801 engages is formed in a portion of the other rotating body that faces the lock pin 801 when the valve timing is at the intermediate angle. Also, when the valve timing is fixed at the intermediate angle, hydraulic fluid stops being supplied to the release chamber, and the lock pin 801 is made to protrude out from the housing space by the urging force of the spring so that it engages with the lock hole 802. Relative rotation of the rotating bodies 300 and 400 is restricted, such that the valve timing becomes fixed at the intermediate angle, by engaging the lock pin 801 with the lock hole 802 in this way.

Incidentally, with the variable valve timing apparatus that has this kind of lock mechanism 800, before the engine is stopped, the rotating bodies 300 and 400 are rotated relative to one another such that the lock pin 801 and the lock hole 802 come into positions that enable them engage with each other, and the lock pin 801 is engaged with the lock hole 802. At this time, the rotating bodies 300 and 400 are rotated relative to one another by adjusting the hydraulic pressure in the advance chamber 510 and the retard chamber 520, and the lock pin 801 is engaged with the lock hole 802 by being made to protrude out by the urging force of the spring, which is accomplished by discharging the hydraulic fluid from the release chamber. Then the engine is stopped while the relative rotation of the rotating bodies 300 and 400 are restricted by the lock mechanism 800 in this way. However, depending on the conditions when the engine is stopped, the engine may be stopped without the relative rotation of the rotating bodies 300 and 400 being restricted by the lock mechanism 800, i.e., without the valve timing being fixed at the intermediate angle. However, the vanes 401 of the second rotating body 400 will rock due to fluctuation in the cam torque when the engine is started, and this rocking will cause the second rotating body 400 to pivot to the advance side and the retard side, which will enable the lock pin 801 to engage with the lock hole 802 when the lock pin 801 and the lock hole 802 become aligned. Thus, in this case as well, the valve timing is able to be fixed at the intermediate angle, though be it slightly after the beginning of engine startup. For example, with the technology described in Japanese Patent Application Publication No. 2009-24659 (JP-A-2009-24659), are various improvements are made to more reliably fix the valve timing using this rocking of the vanes 401, i.e., the pivoting of the second rotating body 400, such as employing a stepped hole for the lock hole 802.

If a large amount of hydraulic fluid remains in the advance chamber or the retard chamber of the variable valve timing mechanism when the engine is started after having been stopped without the valve timing being fixed, it tends to be difficult to fix the valve timing by the rocking of the vanes using the fluctuation in can torque described above because the rocking of the vanes of the second rotating body is impeded by the hydraulic pressure from this hydraulic fluid. More specifically, when the temperature of the hydraulic fluid is low and the viscosity thereof is high, such as during a cold start, this tendency becomes even more pronounced.

Here, the variable valve timing apparatus described in Japanese Patent Application Publication No. 11-159308 (JP-A-11-159308), for example, reduces the resistance when rotating the second rotating body to the advanced side, i.e., when advancing the valve timing, compared to when retarding the valve timing, by forming a communication hole in a portion of the retard chambers that communicates this portion of retard chambers with ambient air, and neither supplying nor discharging hydraulic pressure to or from this portion of retard chambers. As a result, the variable valve timing apparatus described in JP-A-11-159308 attempts to improve responsiveness when advancing the valve timing.

Furthermore, if the engine stops without the valve timing being fixed, the fluctuation of cam torque acting on the camshaft often times results in the rotation phase of the second rotation body ending up becoming the most retarded phase so the valve timing becomes the most retarded. Therefore, with the variable valve timing apparatus described above, the responsiveness when advancing the valve timing can be improved, and the pivoting amount when the second rotating body is advanced can be increased when starting the engine after it has been stopped without the valve timing being fixed, which enables the valve timing to be fixed at the intermediate angle.

In this way, with the variable valve timing apparatus described in JP-A-11-159308, a portion of the retard chambers are effectively made to function as oil chambers, so it is possible to mitigate a situation in which a large amount of hydraulic fluid remains in the retard chamber when the engine is started. However, when this kind of structure is employed, a decrease in responsiveness when quickly retarding the valve timing to a target angle is unavoidable. That is, with the apparatus of the related art, the variable valve timing performance while the engine is operating normally must be sacrificed to a certain degree in order to ensure good engine startability. Therefore, there remains room for improvement in this respect.

SUMMARY OF THE INVENTION

This invention therefore provides a variable valve timing apparatus for an internal combustion engine that is capable of reliably fixing valve timing at an intermediate angle by a lock mechanism during engine startup after the engine has been stopped without the valve timing being fixed, should such a event occur, while suppressing any adverse effects on variable valve timing performance.

A first aspect of the invention relates to a variable valve timing apparatus for an internal combustion engine. This apparatus includes a variable valve timing mechanism that changes a valve timing of at least one of an intake valve or an exhaust valve by changing a relative rotation phase of a camshaft with respect to a crankshaft; and a lock mechanism that fixes the valve timing at an intermediate angle between a most advanced angle and a most retarded angle. The variable valve timing mechanism includes i) a first rotating body and a second rotating body that are rotating bodies that rotate about the same rotational axis, the first rotating body being drivingly connected to the crankshaft and having a plurality of housing chambers surrounding the rotational axis, and the second rotating body being drivingly connected to the camshaft and having a plurality of vanes that extend in a radial direction of the rotational axis and are arranged in the housing chambers, one vane being housed in each housing chamber; ii) an advance chamber formed on one side of the vane in each housing chamber and a retard chamber formed on the other side of the vane in each housing chamber, the advance chambers and the retard chambers serving as hydraulic pressure chambers into which hydraulic fluid is supplied from an oil pump; iii) a discharge passage that extends from each of the hydraulic pressure chambers on the rotational axis side and discharges hydraulic fluid from the hydraulic pressure chambers; and iv) an opening mechanism that communicates the hydraulic pressure chambers with an ambient air space to open the hydraulic pressure chambers to ambient air at least when the first rotating body and the second rotating body have stopped rotating. The opening mechanism places at least one of the hydraulic pressure chambers that is communicated with the discharge passage in a position vertically higher than the rotational axis when the first rotating body and the second rotating body have stopped rotating at a given phase, and from which hydraulic fluid is discharged into the discharge passage, in a state constantly open to ambient air regardless of the phase at which the first rotating body and the second rotating body have stopped.

With a structure in which hydraulic fluid in a hydraulic pressure chamber is discharged through a discharge passage that extends from this hydraulic pressure chamber to the rotational axis side of each rotating body, hydraulic fluid is unable to be discharged to the discharge passage from a hydraulic pressure chamber that is communicated with the discharge passage in a position vertically below the rotational axial center of both rotating bodies when both rotating bodies stop when the engine stops. On the other hand, hydraulic fluid can be discharged to the discharge passage from a hydraulic pressure chamber that is communicated with the discharge passage in a position vertically higher than the rotational axial center of both rotating bodies. However, even though the amount that is discharged from the hydraulic pressure is affected by how tightly closed the hydraulic pressure chamber is (i.e., the oil tightness of the hydraulic pressure chamber), that amount is low.

Therefore, with this invention, when both of the rotating bodies stop rotating at a given phase when the engine stops, the opening mechanism places at least one of the hydraulic pressure chambers that is communicated with the discharge passage in a position vertically higher than the rotational axis when the first rotating body and the second rotating body have stopped rotating at a given phase, and from which hydraulic fluid is discharged into the discharge passage, in a state constantly open to ambient air regardless of the phase at which the rotating bodies have stopped. As a result, ambient air is introduced into the hydraulic pressure chambers that are open to the ambient air, and the hydraulic fluid in the hydraulic pressure chambers is discharged through the discharge passages according to the amount of introduced ambient air. As a result of the hydraulic fluid being discharged from the hydraulic pressure chambers in this way, the hydraulic pressure in the hydraulic pressure chambers that acts on the vane is reduced, thereby making it easier for the vane to rock. Accordingly, the amount that the second rotating body pivots is able to increase. Also, this opening mechanism communicates the hydraulic pressure chamber with the ambient air space at least when both of the rotating bodies are stopped, i.e., the hydraulic pressure chamber is maintained tightly closed (i.e., oil tight) while the engine operating unless there is some other control command, so hydraulic fluid is not discharged. In this way, it is possible to reliably fix the valve timing at the intermediate angle with the lock mechanism when the engine is started, while suppressing adverse effects on variable valve timing performance.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing and further features and advantages of the invention will become apparent from the following description of example embodiments with reference to the accompanying drawings, wherein like numerals are used to represent like elements and wherein:

FIG. 1 is a view showing a frame format of the relationship between a variable valve timing mechanism and a hydraulic fluid supplying mechanism according to a first example embodiment of a variable valve timing apparatus for an internal combustion engine of the invention;

FIG. 2 is a path diagram of supply and discharge paths for hydraulic fluid in the variable valve timing mechanism according to this example embodiment;

FIGS. 3A and 3B are sectional views of the sectional structure of the variable valve timing mechanism according to this example embodiment taken along line DB-DB in FIG. 2, shown laid out on a plane, with FIG. 3A being a sectional view of a state in which hydraulic fluid has been supplied to a lock mechanism, and FIG. 3B being a sectional view of a state in which hydraulic fluid has been discharged from the lock mechanism;

FIGS. 4A and 4B are sectional views of the sectional structure of the variable valve timing mechanism according to this example embodiment taken along line DC-DC in FIG. 2, shown laid out on a plane, with FIG. 4A being a sectional view of a state in which hydraulic fluid has been supplied to an opening mechanism, and FIG. 4B being a sectional view of a state in which hydraulic fluid has been discharged from the opening mechanism;

FIGS. 5A to 5D are views showing frame formats of the sectional structure of the variable valve timing mechanism according to this example embodiment taken along line DB-DB in FIG. 2, shown laid out on a plane;

FIG. 6 is a table showing the relationships among the operating state of the internal combustion engine, the operating states of first and second lock pins, the open/closed states of first and second ambient air communication passages, the operating state of an opening pin, the supply/discharge state of hydraulic fluid with respect to a third release chamber, and the open/closed state of a third ambient air communication passage, for the variable valve timing mechanism according to this example embodiment;

FIG. 7 is a table showing the relationships among the operating state of the internal combustion engine, the operating states of the first and second lock pins, the open/closed states of the first and second ambient air communication passages, the operating state of the opening pin, the supply/discharge state of hydraulic fluid with respect to the third release chamber, and the open/closed state of the third ambient air communication passage, for the variable valve timing mechanism according to a second example embodiment of the variable valve timing apparatus for an internal combustion engine of the invention;

FIG. 8 is a table summarizing the control state of hydraulic fluid with respect to an opening mechanism, a self-advance function, and lock state switchability, for the variable valve timing mechanisms according to the first and second example embodiments of the variable valve timing apparatus for an internal combustion engine of the invention and a variable valve timing mechanism of a variable valve timing apparatus according to related art;

FIGS. 9A to 9C are sectional views of the sectional structure of the variable valve timing mechanism according to another example embodiment of the invention, shown laid out on a plane;

FIGS. 10A and 10B are plan views showing the planar structure of a portion of the variable valve timing mechanism according to still another example embodiment of the invention; and

FIG. 11 is a path diagram of supply and discharge paths for hydraulic fluid in a variable valve timing mechanism of a variable valve timing apparatus according to related art.

DETAILED DESCRIPTION OF EMBODIMENTS First Example Embodiment

A first example embodiment of the variable valve timing apparatus for an internal combustion engine of the invention, in which this variable valve timing apparatus is one that changes the valve timing of an intake valve, will be described with reference to FIGS. 1 to 6. Incidentally, in the description below, the term “valve timing” refers to the valve timing of the intake valve unless otherwise specified.

As shown in FIG. 1, an oil pan 101 in which hydraulic fluid for driving various hydraulically driven auxiliary devices is stored is mounted to a lower portion of an internal combustion engine 10. Meanwhile, a camshaft 31 for driving an intake valve, not shown, open and closed is provided in an upper portion of the internal combustion engine 10, and a variable valve timing apparatus 20 for changing the valve timing is provided on this camshaft 31. The rotational force of a crankshaft 11 is transmitted from a chain 12 to the camshaft 31 of the intake valve via the variable valve timing apparatus 20. The intake valve is driven open and closed by a cam, not shown, formed on the camshaft 31, by rotating the camshaft 31 using the rotational force of the crankshaft 11. Incidentally, the hydraulic fluid stored in the oil pan 101 functions to generate hydraulic pressure for driving the variable valve timing apparatus 20, as well as serves as lubricating oil for lubricating various portions of the internal combustion engine 10.

The variable valve timing apparatus 20 includes a variable valve timing mechanism 40 that changes the valve timing of the intake valve, and a lock mechanism 50 for fixing the valve timing at a specific angle. In addition, the variable valve timing apparatus 20 includes a hydraulic fluid supplying mechanism 100 that supplies hydraulic fluid to the variable valve timing mechanism 40 and the lock mechanism 50, and an electronic control unit (ECU) 120 that controls the operating state of the variable valve timing mechanism 40, i.e., the valve timing, via this hydraulic fluid supplying mechanism 100.

The hydraulic fluid supplying mechanism 100 includes a hydraulic circuit 110 and an oil pump 102. The hydraulic circuit 110 is formed of a plurality of oil passages that supply hydraulic fluid from the oil pan 101 to the variable valve timing b mechanism 40 and the lock mechanism 50, and return hydraulic fluid from the variable valve timing mechanism 40 and the lock mechanism 50 to the oil pan 101. The oil pump 102 draws up hydraulic fluid from the oil pan 101 and supplies it to the hydraulic circuit 110. A first flow control valve 103 that controls the supply and discharge of hydraulic fluid with respect to the variable valve timing mechanism 40, and a second flow control valve 104 that controls the supply and discharge of hydraulic fluid with respect to the lock mechanism 50 and an opening mechanism (see FIG. 2) are provided midway in the hydraulic circuit 110. Incidentally, an engine driven pump that is driven by the crankshaft 11 may be employed as the oil pump 102.

Also, the ECU 120 receives detection signals from a variety of sensors, including a crank angle sensor 121 and a cam angle sensor 122, sets a target angle for a valve timing suitable for the operating state of the engine based on these detection signals, and controls the variable valve timing apparatus 20 such that the actual valve timing comes to match this target angle.

Next, the structure of the variable valve timing mechanism 40 will be described with reference to FIGS. 1 and 2. Incidentally, FIG. 1 is a view of the sectional structure of the variable valve timing mechanism 40 taken along line DA-DA in FIG. 2. Also, FIG. 2 is a view of the planar structure of the variable valve timing mechanism 40 when a cover 42 shown in FIG. 1 has been removed from the variable valve timing mechanism 40. Incidentally, the camshaft 31 and a sprocket 41C rotate in the rotational direction RA shown in FIG. 2.

The variable valve timing mechanism 40 is formed by a first rotating body 41 that rotates in synchronization with the crankshaft 11 via the chain 12, and a second rotating body 43 that rotates in synchronization with the camshaft 31 for the intake valve by being fixed to this camshaft 31.

The first rotating body 41 includes the sprocket 41C that is connected to the crankshaft 11 and rotates in synchronization with the crankshaft 11, a housing 41B that is mounted to the sprocket 41C and rotates together with the sprocket 41C, and the cover 42 that is mounted to the housing 41B. Three dividing walls 41A that protrude radially inward are formed on the housing 41B at substantially equiangular intervals in the circumferential direction.

A boss 43B of the second rotating body 43, that is attached to a center bolt 44, is fixed to an end portion of the camshaft 31. Also, three vanes 43A that protrude radially outward from the outer peripheral surface of the boss 43B are formed at substantially equiangular intervals in the circumferential direction on the boss 43B. Also, three housing chambers 45 are formed surrounding the rotational axis of the camshaft 31 by the inner peripheral surface of the dividing walls 41A of the first rotating body 41 slidably abutting against the output peripheral surface of the boss 43B of the second rotating body 43, with one vane 43A slidably arranged in each housing chamber 45. As a result, each of the housing chambers 45 is divided into an advance chamber 46 and a retard chamber 47 by the corresponding vane 43A.

The relative rotation phase of the first rotating body 41 and the second rotating body 43 of the variable valve timing mechanism 40, i.e., the valve timing, is changed by controlling the supply and discharge (also referred to as the “supply/discharge state”) of hydraulic fluid with respect to the advance chamber 46 and retard chamber 47 via the first flow control valve 103.

Next, the method of changing the valve timing by this variable valve timing mechanism 40 will be described. The valve timing becomes an advanced angle (hereinafter also referred to simply as “advanced”) when the second rotating body 43 rotates in the rotational direction RA with respect to the first rotating body 41 as a result of hydraulic fluid being supplied to the advance chamber 46 and discharged from the retard chamber 47. The valve timing becomes set at the most advanced angle (hereinafter also referred to simply as “most advanced”) when the second rotating body 43 rotates further in the rotational direction RA with respect to the first rotating body 41 and at least one of the vanes 43A abuts against a dividing wall 41A such that the second rotating body 43 is unable to rotate any further (i.e., comes to be in a most advanced phase).

On the other hand, the valve timing becomes a retarded angle (hereinafter also referred to simply as “retarded”) when the second rotating body 43 rotates in direction opposite the rotational direction RA with respect to the first rotating body 41 as a result of hydraulic fluid being supplied to the retard chamber 47 and discharged from the advance chamber 46. The valve timing becomes set at the most retarded angle (hereinafter also referred to simply as “most retarded”) when the second rotating body 43 rotates further in the direction opposite the rotational direction RA with respect to the first rotating body 41 and at least one of the vanes 43A abuts against a dividing wall 41A such that the second rotating body 43 is unable to rotate any further (i.e., comes to be in a most retarded phase).

Also, the lock mechanism 50 that fixes the relative rotation phase of the first and second rotating bodies 41 and 43 at an intermediate phase that is between the most advanced phase and the most retarded phase regardless of the hydraulic pressure in the advance chamber 46 and the retard chamber 47 is provided in the variable valve timing mechanism 40. The valve timing is fixed at an intermediate angle between the most advanced angle and the most retarded angle by the relative rotation phase of the first and second rotating bodies 41 and 43 being fixed at the intermediate phase by the lock mechanism 50 in this way. Incidentally, this intermediate angle is set such that the valve timing and the valve overlap between the intake valve and the exhaust valve are suitable for engine startup and while idling.

Next, the structure of the lock mechanism 50 will be described. The lock mechanism 50 is formed by a pair of mechanisms, i.e., a first lock mechanism 60 and a second lock mechanism 70 (see FIG. 2), each of which has a different function. The first lock mechanism 60 restricts a change in the relative rotation phase of the first and second rotating bodies 41 and 43 to the advance side of the intermediate phase, and the second lock mechanism 70 restricts a change in the relative rotation phase of the first and second rotating bodies 41 and 43 to the retard side of the intermediate phase. Incidentally, the first lock mechanism 60 and the second lock mechanism 70 have generally the same structure, so a description of the structure of the second lock mechanism 70 will be omitted.

The first lock mechanism 60 is provided on one of the three vanes 43A formed on the second rotating body 43. A first housing space 62 that houses a first lock pin 61 is formed, and a first spring 63 that urges the first lock pin 61 toward the first rotating body 41 side such that the end portion of the first lock pin 61 protrudes out from the first housing space 62 is housed in this first housing space 62 (see FIG. 1). Also, a first release chamber 62A to which hydraulic fluid is supplied is formed in a portion of the first housing space 62 on the other side of the first lock pin 61 from the first spring 63. The first lock pin 61 is urged in the direction opposite the urging force of the first spring 63 based on the hydraulic pressure in the first release chamber 62A. Meanwhile, a first lock hole 64 with which the first lock pin 61 can engage when the relative rotation phase of the first and second rotating bodies 41 and 43 is the intermediate phase, i.e., when the valve timing is the intermediate angle, is formed in the first rotating body 41.

With this first lock mechanism 60, when the relative rotation phase of the first and second rotating bodies 41 and 43 is the intermediate phase, hydraulic fluid is discharged from the first release chamber 62A. When the hydraulic pressure decreases as a result, the first lock pin 61 is made to protrude out from the first housing space 62 by the urging force of the first spring 63, and the end portion of the first lock pin 61 engages with the first lock hole 64. That is, the first lock mechanism 60 becomes in a locked state (i.e., locked). When the first lock mechanism 60 is locked in this way, even if torque toward the advance side is applied to the second rotating body 43, the valve liming is restricted from advancing beyond the intermediate angle by the advance side wall surface of the first lock pin 61 engaging with the advance side wall surface of the first lock hole 64. On the other hand, if hydraulic fluid is supplied to the first release chamber 62A such that the hydraulic pressure increases when the first lock mechanism 60 is locked in this way, the first lock pin 61 will be urged by this hydraulic pressure so that it slips out of the first lock hole 64 and becomes housed in the first housing space 62. That is, the first lock mechanism 60 becomes in an unlocked state (i.e., unlocked). When the first lock mechanism 60 is unlocked in this way, the valve timing can be changed to a given angle based on the supply and discharge of hydraulic fluid with respect to the advance chamber 46 and the retard chamber 47.

The second lock mechanism 70 is provided in one of the other two vanes 43A other than the vane 43A in which the first lock mechanism 60 is provided. Just as when restricting or changing the valve timing of the first lock mechanism 60, when the second lock mechanism 70 is locked, even if torque toward the retard side is applied to the second rotating body 43, the valve timing is restricted from retarding beyond the intermediate angle by the retard side wall surface of a second lock pin 71 engaging with the retard side wall surface of the second lock hole 74. On the other hand, when the second lock mechanism 70 is unlocked, the valve timing can be changed to a given angle based on the supply and discharge of hydraulic fluid with respect to the advance chamber 46 and the retard chamber 47.

Incidentally, an opening mechanism 90 is provided in the remaining vane 43A in which neither the first lock mechanism 60 nor the second lock mechanism 70 is provided, as shown in FIG. 2. This opening mechanism 90 is shown in detail in FIGS. 4A and 4B.

Next, the flow of hydraulic fluid between a hydraulic fluid supplying mechanism 100 and the variable valve timing mechanism 40 that includes the lock mechanism 50 and the opening mechanism 90 will be described with reference to FIG. 2. Incidentally, as will be described later, the lock mechanism 50 has an opening function in which it introduces ambient air inside in order to quickly discharge the hydraulic fluid from the hydraulic pressure chambers 46 and 47, just like the opening mechanism 90, in addition to the function of restricting the relative rotation of the first and second rotating bodies 41 and 43.

The hydraulic circuit 110 is formed by a plurality of oil passages, i.e., a first oil supply passage 111, a first oil discharge passage 112, an advance oil passage 113, a retard oil passage 114, a second oil supply passage 115, a second oil discharge passage 116, a first release oil passage 117, a second release oil passage 118, and a third release oil passage 119. Here, the first oil supply passage 111 supplies hydraulic fluid delivered from the oil pump 102 to the first flow control valve 103, while the first oil discharge passage 112 returns hydraulic fluid that has been discharged from the variable valve timing mechanism 40 to the first flow control valve 103 back to the oil pan 101. Incidentally, this first oil discharge passage 112 is formed by an inner wall of the internal combustion engine 10 (such as an inner wall of a chain case) that does not actually have the uniform shape of a pipe or a hole or the like, but instead has a shape suitable for guiding hydraulic fluid to the oil pan 101. Also, the advance oil passage 113 enables hydraulic fluid to flow between the first flow control valve 103 and each advance chamber 46, while the retard oil passage 114 enables hydraulic fluid to flow between the first flow control valve 103 and each retard chamber 47.

Furthermore, the second oil supply passage 115 supplies hydraulic fluid delivered from the oil pump 102 to a second flow control valve 104, while the second oil discharge passage 116 returns hydraulic fluid discharged from the lock mechanism 50 and the opening mechanism 90 to the second flow control valve 104 back to the oil pan 101. Incidentally, this second oil discharge passage 116 is formed by an inner wall of the internal combustion engine 10 or the like, similar to the first oil discharge passage 112. Also, the first release oil passage 117 enables hydraulic fluid to flow between the second flow control valve 104 and the first release chamber. 62A, while the second release oil passage 118 enables hydraulic fluid to flow between the second flow control valve 104 and a second release chamber 72A, and the third release oil passage 119 enables hydraulic fluid to flow between the second flow control valve 104 and a third release chamber 92A to which hydraulic fluid is supplied in the opening mechanism 90.

The advance oil passage 113 and the retard oil passage 114 are separately connected to the advance chamber 46 and the retard chamber 47, respectively. Also, the first release oil passage 117, the second release oil passage 118, and the third release oil passage 119 are separately connected to the first release chamber 62A, the second release chamber 72A, and the third release chamber 92A. That is, the first flow control valve 103 is structured as a valve that enables independent control of the supply and discharge of hydraulic, fluid to and from the advance chamber 46 and the retard chamber 47, while the second flow control valve 104 is structured as a valve that enables independent control of the supply and discharge of hydraulic fluid to and from the first release chamber 62A, the second release chamber 72A, and the third release chamber 92A.

Also, an advance discharge passage 46A, a retard discharge passage 47A, a first discharge passage 62B, a second discharge passage 72B, and a third discharge passage 92B are provided in the boss 43B. The advance discharge passage 46A extends in the radial direction from each advance chamber 46 toward the center bolt 44. The retard discharge passage 47A extends in the radial direction from each retard chamber 47 toward the center bolt 44. The first discharge passage 62B extends in the radial direction from the first release chamber 62A toward the center bolt 44. The second discharge passage 72B extends in the radial direction from the second release chamber 72A toward the center bolt 44, and the third discharge passage 92B extends in the radial direction from the third release chamber 92A toward the center bolt 44. The advance discharge passage 46A is communicated with the first oil discharge passage 112 via the first flow control valve 103. Hydraulic fluid from each advance chamber 46 is discharged to the first oil discharge passage 112 through this advance discharge passage 46A. The retard discharge passage 47A is communicated with the first oil discharge passage 112 via the first flow control valve. 103. Hydraulic fluid in each retard chamber 47 is discharged to the first oil discharge passage 112 through this retard discharge passage 47A. The first discharge passage 62B is communicated with the second oil discharge passage 116 via the second flow control valve 104. Hydraulic fluid in the first release chamber 62A is discharged to the second oil discharge passage 116 through this first discharge passage 62B. The second discharge passage 72B is communicated with the second oil discharge passage 116 via the second flow control valve 104. Hydraulic fluid in the second release chamber 72A is discharged to the second oil discharge passage 116 through this second discharge passage 72B. The third discharge passage 92B is communicated to the second oil discharge passage 116 via the second flow control valve 104. Hydraulic fluid in the third release chamber 92A is discharged to the second oil discharge passage 116 through this third discharge passage 92B.

Here, the relationship between the supply/discharge states of the first flow control valve 103 and the second flow control valve 104 when the valve timing is fixed at the intermediate angle, and the supply/discharge state of hydraulic fluid in the variable valve timing mechanism 40 will be described.

The first flow control valve 103 sets the supply/discharge state of the hydraulic fluid by changing the position of a spool, not shown, housed inside the first flow control valve 103 to a specific position, thereby switching the connection state between the first oil supply passage 111 and the first oil discharge passage 112, and the advance oil passage 113 and the retard oil passage 114. Also, the second flow control valve 104 sets the supply/discharge state of the hydraulic fluid by changing the position of a spool, not shown, housed inside the second flow control valve 104 to a specific position, thereby switching the connection state between the second oil supply passage 115 and the second oil discharge passage 116, and the first release oil passage 117, the second release oil passage 118, and the third release oil passage 119.

Also, when there is a command to fix the valve timing at the intermediate angle, the relative rotation phase of the first and second rotating bodies 41 and 43 is fixed, i.e., the variable valve timing mechanism 40 is placed in a fixed state (hereinafter referred to as a “fixed mode”) by setting the supply/discharge state of the first flow control valve 103 to a mode A, for example, and setting the supply/discharge state of the second flow control valve 104 to a mode B.

In mode A, the advance oil passage 113 and the first oil supply passage 111 are connected together, and the retard oil passage 114 and the first oil discharge passage 112 are connected together. Also, in mode B, the first to third release oil passages 117 to 119 are connected to the second oil discharge passage 116. That is, hydraulic fluid is supplied to the advance chamber 46 and hydraulic fluid is discharged from the retard chamber 47. In addition, hydraulic fluid is also discharged from the release chambers 62A, 72A, and 92A.

When the first flow control valve 103 is set to mode A and the second flow control valve 104 is set to mode B, the rotation phase of the second rotating body 43 attempts to change to the advance side and the lock pins 61 and 72 attempt to displace to the locked state. Therefore, when the rotation phase reaches the intermediate phase as the second rotating body 43 rotates to the advance side, the valve timing will become fixed at the intermediate angle.

The supply/discharge states of the first and second flow control valves 103 and 104 are basically selected according to a command to change the valve timing set based on the engine operating state. For example, when there is a command to fix the valve timing at the intermediate angle in an extremely low load state, including while the engine is stopped or idling, the fixed mode described above is selected.

Incidentally, if the engine has been stopped without the relative rotation phase of the first and second rotating bodies 41 and 43 being fixed at an intermediate phase such as that described above (hereinafter referred to as “when the engine stops abnormally” etc.), the relative rotation phase is fixed at the intermediate phase by the rocking of the vanes 43A, which in turn causes the second rotating body 43 to pivot, as a result of the fluctuation in cam torque when the engine is started next. In this case, if there is a large amount of hydraulic fluid remaining in the advance chamber 46 and the retard chamber 47, the rocking of the, vanes 43A will be impeded by the hydraulic pressure of this hydraulic fluid. As a result, the valve timing may not be able to be quickly fixed at the intermediate angle using the fluctuation in the cam torque.

Therefore, in this example embodiment, a first ambient air communication passage 81 and a second ambient air communication passage 82, each of which communicates the advance chambers 46 and the retard chambers 47 with an ambient air space to open the hydraulic pressure chambers to ambient air, are provided in the first lock mechanism 60 and the second lock mechanism 70, respectively.

Next, the first and second ambient communication passages 81 and 82 provided in the first lock mechanism 60 and the second lock mechanism 70, respectively, will be described in detail referring to FIGS. 3A and 3B. Incidentally, FIGS. 3A and 3B are sectional views of the sectional structure taken along line DB-DB in FIG. 2, shown laid out on a plane.

The first lock mechanism 60 has a first lock hole 64 and a first lock groove 65 that extends on the retard side in the circumferential direction from the first lock hole 64, formed in the sprocket 41C of the first rotating body 41. The depth of the first lock groove 65 is shallower than the depth of the first lock hole 64. Also, a first advance communication passage 66 that communicates the advance chamber 46 with the first housing space 62, and a first retard communication passage 67 that communicates the retard chamber 47 with the first housing space 62 are formed in the vane 43A. Furthermore, a first opening passage 68 that communicates the first housing space 62 with the ambient air space is formed in the vane 43A. The openings of the first advance communication passage 66, the first retard communication passage 67, and the first opening passage 68 in the first housing space 62 are formed in positions in which they are closed off by the first lock pin 61 when the first lock pin 61 is urged to a position in which it abuts against the cover 42 from the hydraulic pressure in the first release chamber 62A. Moreover, the passages 66, 67, and 68 are formed in positions in which they are not closed off by the first lock pin 61 when the first lock pin 61 is being urged by the first spring 63, and when the first lock pin 61 is not engaged with the first lock hole 64 or the first lock groove 65. Also, the first advance communication passage 66 and the first retard communication passage 67 are formed in the same positions in the urging direction of the first spring 63. Incidentally, the first ambient air communication passage 81 is formed by the first advance communication passage 66, the first retard communication passage 67, and the first opening passage 68.

In the first lock mechanism 60 structured as described above, as shown in FIG. 3A, the first advance communication passage 66, the first retard communication passage 67, and the first opening passage 68 are closed off by the first lock pin 61 when the first lock pin 61 is urged in the direction opposite the urging force of the first spring 63 based on hydraulic fluid being supplied to the first release chamber 62A when the internal combustion engine 10 operates. That is, hydraulic fluid in the hydraulic pressure chambers 46 and 47 is not discharged through the first ambient air communication passage 81 when the first lock pin 61 is displaced to a position that closes off the first ambient air communication passage 81.

Also, as shown in FIG. 3B, the first lock pin 61 engages with the first lock hole 64 when the relative rotation phase of the first and second rotating bodies 41 and 43 is the intermediate phase and when the first lock pin 61 is urged by the first spring 63, based on a decrease in the hydraulic pressure in the first release chamber 62A as a result of the supply/discharge state of the second flow control valve 104 being set to mode B, for example. At this time, the first advance communication passage 66, the first retard communication passage 67, and the first opening passage 68 are communicated. That is, the first lock pin 61 is displaced to a position that opens the first ambient air communication passage 81. As a result, ambient air is introduced into the advance chamber 46 and the retard chamber 47 through the first ambient air communication passage 81 when the vane 43A provided with the first ambient air communication passage 81 stops in a position vertically higher than the center bolt 44 when the internal combustion engine 10 stops. Then the hydraulic fluid remaining in the hydraulic pressure chambers 46 and 47 is discharged through the advance discharge passage 46A and the retard discharge passage 47A according to the amount of air that is introduced.

Similarly, the second lock mechanism 70 has a second lock groove 75 that extends on the retard side in the circumferential direction from a second lock hole 74, formed in the first rotating body 41. Also, a second advance communication passage 76 that communicates the advance chamber 46 with the second housing space 72, a second retard communication passage 77 that communicates the retard chamber 47 with the second housing space 72, and a second opening passage 78 that communicates the second housing space 72 with the ambient air space, are formed in the vane 43A. The second advance communication passage 76, the second retard communication passage 77, and the second opening passage 78 are formed in positions in which they are closed off by the second lock pin 71 when the first lock pin 71 is urged to a position in which it abuts against the cover 42 from the hydraulic pressure in the second release chamber 72A. Moreover, the passages 76, 77, and 78 are formed in positions in which they are not closed off by the second lock pin 71 when the second lock pin 71 is being urged by the second spring 73, and when the second lock pin 71 is not engaged with the second lock hole 74 or the second lock groove 75. Also, the second advance communication passage 76 and the second retard communication passage 77 are formed in the same positions in the urging direction of the second spring 73. Incidentally, the second ambient air communication passage 82 is formed by the second advance communication passage 76, the second retard communication passage 77, and the second opening passage 78.

In the second lock mechanism 70 structured as described above, as shown in FIG. 3A, the second advance communication passage 76, the second retard communication passage 77, and the second opening passage 78 are closed off by the second lock pin 71 when the second lock pin 71 is urged in the direction opposite the urging force of the second spring 73, based on hydraulic fluid being supplied to the second release chamber 72A when the internal combustion engine 10 operates. That is, hydraulic fluid in the hydraulic pressure chambers 46 and 47 is not discharged through the second ambient air communication passage 82 when the second lock pin 71 is displaced to a position that closes off the second ambient air communication passage 82.

Also, as shown in FIG. 3B, the second lock pin 71 engages with the second lock hole 74 when the relative rotation phase of the first and second rotating bodies 41 and 43 is the intermediate phase and when the second lock pin 71 is urged by the second spring 73, based on a decrease in the hydraulic pressure in the second release chamber 72A as a result of the supply/discharge state of the second flow control valve 104 being set to mode B, for example. At this time, the second advance communication passage 76, the second retard communication passage 77, and the second opening passage 78 are communicated. That is, the second lock pin 71 is displaced to a position that opens the second ambient air communication passage 82. As a result, ambient air is introduced into the advance chamber 46 and the retard chamber 47 through the second ambient air communication passage 82 when the vane 43A provided with the second ambient air communication passage 82 stops in a position vertically higher than the center bolt 44 when the internal combustion engine 10 stops. Then the hydraulic fluid remaining in the advance chamber 46 and the retard chamber 47 is discharged through the advance discharge passage 46A and the retard discharge passage 47A according to the amount of air that is introduced.

Here, when the variable valve timing mechanism 40 has stopped with the second rotating body 43 that is not provided with the first or second ambient air communication passages 81 or 82 in a position vertically higher than the center bolt 44 when the engine has stopped abnormally, it may be difficult to fix the valve timing at the intermediate angle using the rocking of the vanes 43A of the second rotating body 43 when the engine is started, with the advance chamber 46 and the retard chamber 47 on both sides of the vane 43A, like the case described above.

Therefore, in this example embodiment, the vane 43A with neither the first lock mechanism 60 nor the second lock mechanism 70 is provided with the opening mechanism 90 that opens the advance chamber 46 and the retard chamber 47 on both sides of the vane 43A to ambient air.

This opening mechanism 90 will now be described in detail with reference to FIGS. 4A and 4B. FIGS. 4A and 4B are sectional views of the sectional structure taken along line DC-DC in FIG. 2, shown laid out on a plane. The opening mechanism 90 has a third housing space 92 in which an opening pin 91 is housed. A third spring 93 that urges the opening pin 91 toward the first rotating body 41 side is also housed in the third housing space 92. Also, the third release chamber 92A to which hydraulic fluid is supplied is formed in a portion of the third housing space 92 that is on the opposite side of the opening pin 91 from the third spring 93. The opening pin 91 is urged in the direction opposite the urging force of the third spring 93 based on the hydraulic pressure of the third release chamber 92A. Also, a third advance communication passage 94 that communicates the advance chamber 46 with the third housing space 92 is provided in the vane 43A with the opening mechanism 90. Further, a third retard communication passage 95 that communicates the retard chamber 47 with the third housing space 92, and a third opening passage 96 that communicates the third housing space 92 with the ambient air space are formed. The third advance communication passage 94, the third retard communication passage 95, and the third opening passage 96 are formed in positions in which they are closed off by the opening pin 91 when the opening in 91 is urged to a position in which it abuts against the cover 42 from the hydraulic pressure in the third release chamber 92A. Moreover, the passages 94, 95, and 96 are formed in positions in which they are not closed off by the opening pin 91 even when the opening pin 91 is being urged by the third spring 93. Also, the third advance communication passage 94 and the third retard communication passage 95 are formed in the same positions in the urging direction of the third spring 93. Incidentally, a third ambient air communication passage 83 is formed by the third advance communication passage 94, the third retard communication passage 95, and the third opening passage 96.

In the opening mechanism 90 structured as described above, as shown in FIG. 4A, the third advance communication passage 94, the third retard communication passage 95, and the third opening passage 96 are closed off by the opening pin 91 when the opening pin 91 is urged in the direction opposite the urging force of the third spring 93, based on hydraulic fluid being supplied to the third release chamber 92A when the internal combustion engine 10 operates. That is, hydraulic fluid in the hydraulic pressure chambers 46 and 47 is not discharged through the third ambient air communication passage 83 when the opening pin 91 is displaced to a position in which it closes off the third ambient air communication passage 83.

Also, as shown in FIG. 4B, the third advance communication passage 94, the third retard communication passage 95, and the third opening passage 96 are communicated when the opening pin 91 is urged by the third spring 93 based on a decrease in the hydraulic pressure in the third release chamber 92A as a result of the supply/discharge state of the second flow control valve 104 being set to mode B, for example. That is, the opening pin 91 is displaced to a position that opens the third ambient air communication passage 83. As a result, ambient air is introduced into the advance chamber 46 and the retard chamber 47 through the third ambient air communication passage 83 when the vane 43A provided with the third ambient air communication passage 83 stops in a position vertically higher than the center bolt 44 when the internal combustion engine 10 stops. Then the hydraulic fluid remaining in the hydraulic pressure chambers 46 and 47 is discharged through the advance discharge passage 46A and the retard discharge passage 47A according to the amount of air that is introduced.

Next, a mode in which the valve timing is fixed to the intermediate angle by the lock mechanism 50 when the engine has stopped abnormally will be described with reference to FIGS. 5A to 5D. Incidentally, FIG. 5A to 5D are views showing frame formats of the sectional structure taken along line DB-DB in FIG. 2, shown laid out on a plane.

In order to ensure good engine startability through control of the variable valve timing mechanism 40, the valve timing must always be maintained at an intermediate angle at the beginning of a startup operation of the internal combustion engine 10. Therefore, with this internal combustion engine 10, when an engine stop command is generated following a switching operation of the ignition switch while the engine is operating, the valve timing is fixed at an intermediate angle by the lock mechanism 50 in preparation for the next time the engine is started. That is, when the engine is stopped normally, the lock mechanism 50 fixes the valve timing to the intermediate angle before the internal combustion engine 10 stops in response to an engine stop command. Then operation of the internal combustion engine 10 stops in response to the engine stop command. However, when the engine stops abnormally, the valve timing that is fixed before the engine stops normally is not fixed, and as a result, the startability the next time the engine is started decreases.

Regarding this, according to the lock mechanism 50 of the variable valve timing mechanism 40, the valve timing is fixed to the intermediate angle in the manner described below when the engine is started after stopping abnormally. Here, a case will be assumed in which a startup operation of the internal combustion engine 10 is started while the relative rotation phase of the first and second rotating bodies 41 and 43 is to the retard side of an intermediate phase when the engine stops abnormally.

In this case, when the first lock pin 61 is displaced to a position corresponding to the first lock groove 65 by the second rotating body 43 pivoting to the advance side as the cam torque fluctuates, the first lock pin 61 protrudes from the vane 43A and the tip end portion of the first lock pin 61 fits into the first lock groove 65, as shown in FIG. 5A.

Then, while the tip end portion of the first lock pin 61 is in the first lock groove 65, the first lock pin 61 moves in the first lock groove 65 to the advance side as the second rotating body 43 continues to be displaced to the advance side.

In this state, when the second lock pin 71 is displaced to a position corresponding to the second lock groove 75, the second lock pin 71 protrudes from the vane 43A and the tip end portion of the second lock pin 71 fits into the second lock groove 75, as shown in FIG. 5B.

Furthermore, when the first lock pin 61 is displaced to a position corresponding to the first lock hole 64 as the second rotating body 43 is displaced to the advance side, the first lock pin 61 protrudes from the vane 43A and the tip end portion of the first lock pin 61 fits into the first lock hole 64, as shown in FIG. 5C.

Then in this state, when the second lock pin 71 is displaced to a position corresponding to the second lock hole 74, the second lock pin 71 protrudes from the vane 43A and the tip end portion of the second lock pin 71 fits into the second lock hole 74, as shown in FIG. 5D.

In this way, the second rotating body 43 is restricted from pivoting to the advance side as a result of fluctuation in the cam torque by the advance side wall surface of the first lock pin 61 engaging with the advance side wall surface of the first lock hole 64. The second rotating body 43 is also restricted from pivoting to the retard side as a result of fluctuation in the cam torque by the retard side wall surface of the second lock pin 71 engaging with the retard side wall surface of the second lock hole 74. As a result, the relative rotation phase of the first rotating body 41 and the second rotating body 43 is restricted to the intermediate phase.

Here, the valve timing may not be fixed to the intermediate angle by the lock mechanism 50, as described above, if there is a large amount of hydraulic fluid remaining in the advance chamber 46 and the retard chamber 47 when the startup operation of the internal combustion engine 10 is started.

Regarding this, according to the variable valve timing mechanism 40 of this example embodiment, regardless of the position in which the variable valve timing mechanism 40 stops during an abnormal engine stop, the advance chamber 46 and the retard chamber 47 that are positioned vertically higher than the center bolt 44 become open to the ambient air through at least one of the first, second, or third ambient air communication passages 81, 82, and 83 as a result of a decrease in the hydraulic pressure in the release chambers 62A, 67A, and 92A. As a result, hydraulic fluid is discharged from the hydraulic pressure chambers 46 and 47 through the discharge passages 46A and 47A while the engine is stopped, so cases in which a large amount of hydraulic fluid remains in all of the advance chambers 46 and retard chambers 47 the next time the engine is started are less frequent. Therefore, the valve timing can be quickly fixed to the intermediate angle by the lock mechanism 50 when the engine is started after stopping abnormally.

FIG. 6 is a table showing the relationships among the operating state of the internal combustion engine, the operating states of the first and second lock pin 61 and 71, the open/closed states of the first and second first ambient air communication passages 81 and 82, the operating state of the opening pin 91, the supply/discharge state of hydraulic fluid with respect to the third release chamber 92A, and the open/closed state of the third ambient air communication passage 83.

When the internal combustion engine 10 stops and the hydraulic fluid is discharged from the release chambers 62A, 72A, and 92A based on the supply/discharge state of the second flow control valve 104 being set to mode B, the first and second lock pins 61 and 71 and the opening pin 91 are displaced in the urging direction of the springs 63, 73, and 93 (denoted as “protruding” in the drawing). As a result, the advance communication passages 66, 76, and 94, the retard communication passages 67, 77, and 95, and the opening passages 68, 78, and 96 are communicated, respectively, such that the first, second, and third ambient air communication passages 81, 82, and 83 become open. In this case, hydraulic fluid remaining in the advance chamber 46 and the retard chamber 47 that are positioned vertically higher than the center bolt 44 is discharged through the discharge passages 46A and 47A.

Meanwhile, when hydraulic fluid is supplied to the release chambers 62A, 72A, and 92A when the internal combustion engine 10 is operated, the first and second lock pins 61 and 71 and the opening pin 91 are displaced in the direction opposite the urging force of the springs 63, 73, and 93 (denoted as “housed” in the drawing). As a result, the advance communication passages 66, 76, and 94, the retard communication passages 67, 77, and 95, and the opening passages 68, 78, and 96 are closed off by the pins 61, 71, and 91, respectively, such that the first, second, and third ambient air communication passages 81, 82, and 83 become closed. In this case, even if the advance chamber 46 and the retard chamber 47 are positioned vertically higher than the center bolt 44, hydraulic fluid will not be discharged through the discharge passages 46A and 47A.

Incidentally, when there is a command to fix the valve timing at the intermediate angle while the engine is operating, the supply/discharge state of the second flow control valve 104 is set to mode B. Therefore, even though the engine is operating, the first, second, and third ambient air communication passages 81, 82, and 83 become open as a result of hydraulic fluid being discharged from the release chambers 62A, 72A, and 92A, so hydraulic fluid remaining in the advance chamber 46 and the retard chamber 47 that are positioned vertically higher than the center bolt 44 will be discharged through the through the discharge passages 46A and 47A.

The variable valve timing apparatus for an internal combustion engine according to this example embodiment yields the following effects. (1) When the first and second rotating bodies 41 and 43 stop rotating at a given phase when the engine stops, the advance chamber 46 and the retard chamber 47 that are positioned vertically higher than the rotational axial center of the camshaft 31 are communicated with the ambient air space by at least one of the first and second lock mechanisms 60 and 70 or the opening mechanism 90, and thus become open to ambient air, regardless of the phase in which the first and second rotating bodies 41 and 43 are stopped. As a result, ambient air is introduced into the hydraulic pressure chambers 46 and 47 that are open to the ambient air, and the hydraulic fluid in the hydraulic pressure chambers 46 and 47 is discharged through the discharge passages 46A and 47A according to the amount of introduced ambient air. As a result of the hydraulic fluid being discharged from the hydraulic pressure chambers 46 and 47 in this way, the hydraulic pressure in the hydraulic pressure chambers 46 and 47 that acts on the vane 43A is reduced, thereby making it easier for the vane 43A to rock. Accordingly, the amount that the second rotating body 43 pivots increases, which enables the valve timing to be reliably fixed at the intermediate angle by the lock mechanism 50 when the engine is started.

(2) Also, when the engine stops and when the engine idles as it stops, the ambient air communication passages 81, 82, and 83 communicate the hydraulic pressure chambers 46 and 47 with the ambient air space. That is, while the engine is operating, unless the engine is idling as it stops, the hydraulic pressure chambers 46 and 47 remain tightly closed (i.e., oil tight), so no hydraulic fluid will be discharged. In this way, it is possible to reliably fix the valve timing at the intermediate angle with the lock mechanism when the engine is started, while suppressing adverse effects on variable valve timing performance.

(3) The retard chamber 47 that is positioned vertically higher than the rotational axial center of the camshaft 31 is able to be open to ambient air via one of the ambient air communication passages 81, 82, or 83. As a result, the valve timing can be more quickly fixed at the intermediate angle the next time the engine is started after stopping abnormally.

(4) The advance chamber 46 that is positioned vertically higher than the rotational axial center of the camshaft 31 is able to be open to ambient air via one of the ambient air communication passages 81, 82, or 83. As a result, the next time the engine is started after an abnormal engine stop, the advance chamber 46 can be maintained at substantially atmospheric pressure, which inhibits the rocking of the vane 43A from being restricted due to the effect of negative pressure generated in the advance chamber 46, thus enabling the valve timing to be quickly fixed at the intermediate angle by the lock mechanism 50.

(5) The advance chamber 46 and the retard chamber 47 that are divided by one vane 43A are both able to be open to ambient air. As a result, hydraulic fluid remaining in the retard chamber 47 that is positioned vertically higher than the rotational axial center of the camshaft 31 can be quickly discharged via the retard discharge passage 47A, while the pressure inside the advance chamber 46 remains at substantially atmospheric pressure, which enables the generation of negative pressure when the second rotating body 43 rocks to be suppressed. Accordingly, the air pressure and the hydraulic pressure in the hydraulic pressure chambers 46 and 47 make it possible to suitably inhibit the rocking of the vane 43A from being restricted. As a result, the amount that the second rotating body 43 pivots can be increased, so the valve timing can be quickly fixed at the intermediate angle.

(6) The lock mechanism 50 functions to both discharge the hydraulic fluid in the hydraulic pressure chambers 46 and 47 through the discharge passages 46A and 47A by opening the advance chamber 46 and the retard chamber 47 to the ambient air space, and fix the valve timing at the intermediate angle. As a result, there is no need to newly provide a mechanism (i.e., an opening mechanism) that serves only to open the hydraulic pressure chambers 46 and 47 to the ambient air space. That is, hydraulic fluid can be suitably discharged from the advance chamber 46 and the retard chamber 47 when the engine is stopped, using a pre-existing mechanism (i.e., the lock mechanism).

(7) The first lock groove 65 and the second lock groove 75 are provided as grooves that are shallower than the first lock hole 64 and the second lock hole 74, respectively, and that extend from the first lock hole 64 and the second lock hole 74, respectively, to a predetermined position on the retard side. As a result, when the relative rotation phase of the first rotating body 41 and the second rotating body 43 is to the retard side of the first lock groove 65, the lock pins 61 and 71 engage with the first lock hole 64 and the second lock hole 74, respectively, in that order after being restricted by the first lock groove 65 and the second lock groove 75 in that order when the lock pins 61 and 71 are displaced in the urging direction of the springs 63 and 73 and when the vane 43A rocks due to fluctuation in the can torque. Therefore, the lock pins 61 and 71 engage with the lock holes 64 and 74, respectively, more quickly than they do when the rotation phase is not restricted, so the valve timing is able to be quickly fixed at the intermediate angle.

(8) The intermediate angle of the lock mechanism 50 is set to a value appropriate for an extremely low load state that includes when the engine is stopped and when the engine is idling, and the lock mechanism 50 becomes locked before the engine stops. Accordingly, the internal combustion engine 10 can be started again at a valve timing that is suitable for starting the engine. As a result, good engine startability can be ensured, and the engine will be able to idle stably after the engine is started.

(Second example embodiment) A second example embodiment of the invention will be described with reference to FIGS. 1, 2 and 7, focusing mainly on the differences from the first example embodiment described above. Incidentally, descriptions of structure common with the first example embodiment will be omitted.

The opening mechanism 90 according to the first example embodiment is configured such that the supply and discharge of the hydraulic fluid to and from the third release chamber 92A is controlled by the second flow control valve 104. In contrast, in this example embodiment, hydraulic fluid is supplied and discharged to and from the third release chamber 92A in conjunction with the engine oil pressure, i.e., the oil pressure supplied to the internal combustion engine 10.

The third release chamber 92A in this example embodiment is configured such that hydraulic fluid flows directly between the oil pan 101 and the oil pump 102 without passing through the second flow control valve 104, as shown by the alternate long and short dashes lines in FIGS. 1 and 2. That is, hydraulic fluid that is discharged at a predetermined pressure from the oil pump 102 driven by the internal combustion engine 10 as the engine operates is supplied to the third housing space 92 by the oil pump 102 being driven. Accordingly, when the opening pin 91 is urged in a direction opposite the urging force of the third spring 93, the third advance communication passage 94, the third retard communication passage 95, and the third opening passage 96 are closed off by the opening pin 91. That is, when the opening pin 91 is displaced to a position in which it closes off the third ambient air communication passage 83, hydraulic fluid in the hydraulic pressure chambers 46 and 47 will not be discharged through the third ambient air communication passage 83.

Therefore, even if there is a command to fix the valve timing at the intermediate angle while the engine is operating, hydraulic fluid is constantly supplied to the third release chamber 92A based on the hydraulic pressure from the oil pump 102 when the vane 43A provided with the opening mechanism 90 stops in a position vertically higher than the center bolt 44. Therefore, as described above, hydraulic fluid in the hydraulic pressure chambers 46 and 47 will not be discharged through the third ambient air communication passage 83. Thus, the phase of the second rotating body 43 can be maintained at the intermediate angle by the hydraulic pressure in the hydraulic pressure chambers 46 and 47, which enables the characteristic in which the lock mechanism 50 quickly changes to a locked state (hereinafter simply referred to as “lock state switchability”) to be improved.

Incidentally, when the engine stops, hydraulic fluid is discharged from the advance chamber 46 and the retard chamber 47, similar to the first example embodiment, so the rotation phase of the second rotating body 43 is able to be advanced to the intermediate phase by sufficiently using the fluctuation in the cam torque the next time the engine is started after stopping abnormally (hereinafter this will be referred to as a “self-advance function”). As a result, the valve timing can be quickly fixed at an intermediate angle.

FIG. 7 is a table summarizing the relationships among the operating state of the internal combustion engine 10, the operating states of first and second lock pins 61 and 71, the open/closed states of first and second ambient air communication passages 81 and 82, the operating state of the opening pin 91, the supply/discharge state of hydraulic fluid with respect to the third release chamber 92A, and the open/closed state of the third ambient air communication passage 83.

When the internal combustion engine 10 stops and hydraulic fluid is discharged from the release chambers 62A and 72A based on the supply/discharge state of the second flow control valve 104 being set to mode B, and hydraulic fluid is discharged from the third release chamber 92A due to the loss of engine oil pressure, the first and second lock pins 61 and 72 and the opening pin 91 are displaced in the urging direction of the springs 63, 73, and 93 (denoted as “protruding” in the drawing). As a result, the advance communication passages 66, 76, and 94, the retard communication passages 67, 77, and 95, and the opening passages 68, 78, and 96 are communicated, respectively, such that the first, second, and third ambient air communication passages 81, 82, and 83 become open. In this case, hydraulic fluid remaining in the advance chamber 46 and the retard chamber 47 that are positioned vertically higher than the center bolt 44 is discharged through the discharge passages 46A and 47A.

Meanwhile, when hydraulic fluid is supplied to the release chambers 62A, 72A, and 92A when the internal combustion engine 10 is operated, the first and second lock pins 61 and 71 and the opening pin 91 are displaced in the direction opposite the urging force of the springs 63, 73, and 93 (denoted as “housed” in the drawing). As a result, the advance communication passages 66, 76, and 94, the retard communication passages 67, 77, and 95, and the opening passages 68, 78, and 96 are closed off by the pins 61, 71, and 91, respectively, such that the first, second, and third ambient air communication passages 81, 82, and 83 become closed. In this case, even if the advance chamber 46 and the retard chamber 47 are positioned vertically higher than the center bolt 44, hydraulic fluid will not be discharged through the discharge passages 46A and 47A.

Incidentally, when there is a command to fix the valve timing at the intermediate angle while the engine is operating, the supply/discharge state of the second flow control valve 104 is set to mode B. Therefore, even though the engine is operating, the first and second ambient air communication passages 81 and 82 become open as a result of hydraulic fluid being discharged from the release chambers 62A and 72A. As a result, when the vanes 43A provided with the first lock mechanism 60 and the second lock mechanism 70 are positioned vertically higher than the center bolt 44, hydraulic fluid in the advance chambers 46 and the retard chambers 47 that are on both sides the vanes 43A is discharged through the discharge passages 46A and 47A.

On the other hand, when the engine is operating, hydraulic fluid is constantly supplied to the third release chamber 92A because the oil pump 102 is being driven, so the opening mechanism 90 is closed. That is, when the vane 43A provided with the opening mechanism 90 stops in a position vertically higher than the center bolt 44, the advance chamber 46 and the retard chamber 47 that are on both sides of the vane 43A will not become open to the ambient air space, so the hydraulic pressure in the hydraulic pressure chambers 46 and 47 can be maintained.

FIG. 8 is a table summarizing the control state of hydraulic fluid with respect to the opening mechanism 90, and the self-advance function and the lock state switchability of the variable valve timing mechanism 40 according to the first example embodiment, the variable valve timing mechanism 40 according to the second example embodiment, and a variable valve timing mechanism without the opening mechanism 90.

In the first example embodiment (see FIG. 6), the supply/discharge state of hydraulic fluid with respect to the third release chamber 92A of the opening mechanism 90 is controlled by the second flow control valve 104. That is, when the supply/discharge state of the second flow control valve 104 is set to mode B when there is a command to fix the valve timing at the intermediate angle while the internal combustion engine 10 is operating, for example, hydraulic fluid in the release chambers 62A, 72A, and 92A circulates to the oil pan 101 via the release oil passages 117, 118, and 119. As a result, the hydraulic fluid in the advance chamber 46 and the retard chamber 47 that are positioned vertically higher than the center bolt 44 is discharged. Incidentally, the hydraulic fluid in the advance chamber 46 and the retard chamber 47 that are positioned vertically higher than the center bolt 44 is also discharged when the engine is stopped. Accordingly, the self-advance function at engine startup can be displayed, but not much can be expected of the lock state switchability by the hydraulic pressure in the hydraulic pressure chambers 46 and 47.

In the second example embodiment (see FIG. 7), the supply/discharge state of hydraulic fluid with respect to the third release chamber 92A of the opening mechanism 90 is controlled in conjunction with the engine oil pressure. That is, when there is a command to fix the valve timing at the intermediate angle while the internal combustion engine 10 is operating, hydraulic fluid in the third release chamber 92A will not be discharged even if the supply/discharge state of the second flow control valve 104 is set to mode B. Therefore, when the vane 43A that is provided with the opening mechanism 90 is positioned vertically higher than the center bolt 44, hydraulic fluid will not be discharged from the advance chamber 46 and the retard chamber 47 that are positioned on both sides of this vane 43A. Incidentally, when the engine is stopped, hydraulic fluid is discharged from the advance chamber 46 and the retard chamber 47 that are positioned vertically higher than the center bolt 44, via the first, second, and third ambient air communication passages 81, 82, and 83. Therefore, the self-advance function at engine startup can be displayed. In addition, when the vane 43A that is provided with the opening mechanism 90 stops in a position vertically higher than the center bolt 44, hydraulic fluid is not discharged from the advance chamber 46 and the retard chamber 47 that are positioned on both sides of this vane 43A, so the lock state switchability by the hydraulic pressure in the hydraulic pressure chambers 46 and 47 increases.

Incidentally, with a variable valve timing mechanism not provided with the opening mechanism 90, when the vanes 43A not provided with the first lock mechanism 60 and the second lock mechanism 70 stop in positions higher than the center bolt 44 when the engine stops, hydraulic fluid is not able to be sufficiently discharged from the advance chambers 46 and the retard chambers 47 that are positioned on both sides of the corresponding vanes 43A, so the self-advance function at engine startup cannot be expected. On the other hand, even if the supply/discharge state of the second flow control valve 104 is set to mode B while the engine is operating, if the remaining 43A on which neither the first lock mechanism 60 nor the second lock mechanism 70 is provided is positioned vertically higher than the center bolt 44, hydraulic fluid will not be discharged from the advance chamber 46 and the retard chamber 47 on both sides of this vane 43A, so the lock state switchability by the hydraulic pressure in the hydraulic pressure chambers 46 and 47 increases.

The example embodiment described above is able to yield the following effects in addition to the effects (1) to (8) of the first example embodiment described above. (9) The opening pin 91 is displaced to a position that closes off the third ambient air communication passage 83 based on the hydraulic pressure of the hydraulic fluid supplied from the oil pump 102 while the engine is operating. On the other hand, the opening pin 91 is displaced to a position that opens the third ambient air communication passage 83 based on the supply of hydraulic fluid from the oil pump 102 being stopped as a result of the engine stopping. Therefore, there is no need to separately provide a driving source for displacing the opening pin 91, so the structure of the opening mechanism 90 can be simplified.

(10) When the valve timing is fixed to the intermediate angle by activating the lock mechanism 50 to restrict the relative rotation of both the rotating bodies 41 and 43 while the engine is operating, such as while the engine is idling, hydraulic fluid is supplied from the oil pump 102 to the opening mechanism 90, such that communication between the hydraulic pressure chambers 46 and 47 and the ambient air space is closed off by the opening pin 91. Therefore, even if the lock mechanism 50 is in a locked state while the engine is operating, with the opening mechanism 90, hydraulic fluid in the hydraulic pressure chambers 46 and 47 that are positioned vertically higher than the rotational axial center of the camshaft 31 will not be discharged through the discharge passages 46A and 47A. Instead, the hydraulic pressure chambers 46 and 47 are maintained tightly closed (i.e., oil tight). As a result, relative rotation of both the rotating bodies 41 and 43 is also restricted by the hydraulic pressure in the hydraulic pressure chambers 46 and 47 on both sides of the vane 43A that is provided with the opening mechanism 90, in addition to the lock mechanism 50, so the valve timing can be more reliably fixed at the intermediate angle.

Other Example Embodiments

Incidentally, the example embodiments of this invention are not limited to the example embodiments described above. That is, the invention may also be carried out in the modes described below, for example. Also, the modified examples below may not only be applied to the example embodiments described above, but may also be carried out in combination with each other.

In the first example embodiment described above, the structure is such that the supply/discharge state of hydraulic fluid with respect to the advance chamber 46 and the retard chamber 47 is controlled by the first flow control valve 103, and the supply/discharge state of the hydraulic fluid with respect to the first release chamber 62A, the second release chamber 72A, and the third release chamber 92A is controlled by the second flow control valve 104. However, the structure of the flow control valve for controlling the supply/discharge state of hydraulic fluid with respect to the chambers is not limited to this. That is, a single flow control valve may be provided that controls the supply/discharge state of hydraulic fluid with respect to the advance chamber 46, the retard chamber 47, the first release chamber 62A, the second release chamber 72A, and the third release chamber 92A. Alternatively, a first flow control valve may be provided that controls the supply/discharge state of hydraulic fluid with respect to the advance chamber 46, the retard chamber 47, first release chamber 62A, and the second release chamber 72A, and a second flow control valve may be provided that controls the supply/discharge of hydraulic fluid with respect to the third release chamber 92A. With this structure as well, the operation and effects of (1) to (8) described above are also able to be obtained.

In the example embodiments described above, the advance communication passages 66, 76, and 94 and the retard communication passages 67, 77, and 95 are formed in the same position in the urging direction of the springs 63, 73, and 93, respectively, but the positions in which the advance communication passages 66, 76, and 94 and the retard communication passages 67, 77, and 95 are formed are not limited to this. That is, the advance communication passages 66, 76, and 94 may be formed on the first rotating body 41 side of the retard communication passages 67, 77, and 95, or conversely, the retard communication passages 67, 77, and 95 may be formed on the first rotating body 41 side of the advance communication passages 66, 76, and 94. A case in which this modified example is applied to the opening mechanism 90, for example, will be described with reference to FIGS. 9A to 9C.

As shown in FIG. 9A, when the opening pin 91 is urged to a position in which it abuts against the cover 42 by the hydraulic pressure in the third release chamber 92A, the third advance communication passage 94, the third retard communication passage 95, and the third opening passage 96 are closed off by the opening pin 91. As a result, even if the vane 43A that is provided with the opening mechanism 90 stops in a position vertically higher than the center bolt 44, hydraulic fluid in the advance chamber 46 and the retard chamber 47 that are positioned on both sides of this vane 43A will not be discharged through the discharge passages 46A and 47A.

Next, when the hydraulic pressure in the third release chamber 92A decreases such that the opening pin 91 is displaced to a position such as that shown in FIG. 9B, the third retard communication passage 95 is communicated with the third opening passage 96 such that only the retard chamber 47 becomes open to the ambient air. At this time, when the vane 43A that is provided with the opening mechanism 90 stops in a position that is vertically higher than the center bolt 44, hydraulic fluid in the retard chamber 47 next to this vane 43A will be discharged through the retard discharge passage 47A. On the other hand, the third advance communication passage 94 is closed off by the opening pin 91, so hydraulic fluid in the advance chamber 46 will not be discharged. In this way, when only hydraulic fluid in the retard chamber 47 is discharged, even if the rotation phase of the second rotating body 43 is displaced to the most retarded phase when the engine stops abnormally, hydraulic fluid can be appropriately discharged from the retard chamber 47, so the valve timing can be quickly fixed at the intermediate angle using the fluctuation in the cam torque when the engine is started the next time.

Also, when the hydraulic pressure in the third release chamber 92A decreases further such that the opening pin 91 is displaced to a position such as that shown in FIG. 9C, the third advance communication passage 94, the third retard communication passage 95, and the third opening passage 96 are communicated, such that the hydraulic pressure chambers 46 and 47 become open to the ambient air. At this time, when the vane 43A that is provided with the opening mechanism 90 stops in a position that is vertically higher than the center bolt 44, hydraulic fluid in the hydraulic pressure chambers 46 and 47 next to this vane 43A will be discharged through the discharge passages 46A and 47A. With this structure as well, the operation and effects of (1) to (10) described above are also able to be obtained.

In the example embodiments described above, the first, second, and third ambient air communication passages 81, 82, and 83 are provided in the vanes 43A, but the locations where ambient air communication passages are provided is not limited to this. For example, they may also be provided in the first rotating body 41. This kind of structure will now be described with reference to FIGS. 10A and 10B. Incidentally, hereinafter, the structure described below is such that an opening mechanism 200 is positioned vertically higher than the center bolt 44 when the relative rotation of the first and second rotating bodies 41 and 43 stops.

As shown in FIG. 10A, the opening mechanism 200 has a housing chamber 201, an advance communication passage 204, and a retard communication passage 205 formed in the dividing wall 41A. The housing chamber 201 houses a spring 202 and a valve body 203 that is urged toward the center bolt 44 by the spring 202. The advance communication passage 204 communicates the housing chamber 201 with the advance chamber 46, and the retard communication passage 205 that communicates the housing chamber 201 with the retard chamber 47. Also, the housing chamber 201 is formed open to the ambient air space. That is, when the first rotating body 41 rotates in the rotational direction RA when the internal combustion engine 10 operates, the valve body 203 is urged in the opposite direction of the center bolt 44 by centrifugal force. As a result, the housing chamber 201 is closed off from the advance communication passage 204 and the retard communication passage 205 by the valve body 203.

On the other hand, when the first rotating body 41 stops rotating when the internal combustion engine 10 stops, the valve body 203 is urged by the spring 202 so as to be displaced to the position shown in FIG. 10B. At this time, the housing chamber 201 that is communicated with the ambient air space becomes communicated with the advance communication passage 204 and the retard communication passage 205. That is, the opening mechanism 200 becomes open. As a result, ambient air is introduced into the advance chamber 46 and the retard chamber 47 through the opening mechanism 200. Also, hydraulic fluid remaining in the hydraulic pressure chambers 46 and 47 is discharged through the advance discharge passage 46A and the retard discharge passage 47A according to the amount of air that is introduced.

In the example embodiments described above, the advance chambers 46 and the retard chambers 47 are able to be placed in states open to ambient air by providing the advance communication passages 66, 76, and 94, the retard communication passages 67, 77, and 95, and the opening passages 68, 78, and 96, but the hydraulic pressure chambers that are placed in states open to ambient air are not limited to this. That is, only the advance chambers 46 may be placed in a state open to ambient air by providing only the advance communication passages 66, 76, and 94 and the opening passages 68, 78, and 96. With this structure as well, the operation and effects described in (1), (2), (4), and (6) to (10) described above are able to be obtained. In this case, the advance chambers 46 can be maintained at substantially atmospheric pressure, which inhibits the rocking of the vanes 43A from being restricted due to the effect of negative pressure generated in the advance chambers 46, thus enabling the valve timing to be quickly fixed at the intermediate angle by the lock mechanism 50.

In the example embodiments described above, the advance chambers 46 and the retard chambers 47 are able to be placed in states open to ambient air by providing the advance communication passages 66, 76, and 94, the retard communication passages 67, 77, and 95, and the opening passages 68, 78, and 96, but the hydraulic pressure chambers that are placed in states open to ambient air are not limited to this. That is, only the retard chambers 47 may be placed in a state open to ambient air by providing only the retard communication passages 67, 77, and 95 and the opening passages 68, 78, and 96. With this structure as well, the operation and effects described in (1), (2), (3), and (6) to (10) described above are able to be obtained. In this case, even if the rotation phase of the second rotating body 43 is displaced to the most retarded phase when the engine stops abnormally, hydraulic fluid can be appropriately discharged from the retard chambers 47, so the valve timing can be quickly fixed at the intermediate angle using the fluctuation in the cam torque when the engine is started the next time.

In the example embodiments described above, the opening passages 68, 78, and 96 are formed on the retard chamber 47 side sandwiching the housing spaces 62, 72, and 92 in the vanes 43A, but the positions where the opening passages 68, 78, and 96 are formed are not limited to these. That is, they may also be formed on the advance chamber 46 side sandwiching the housing spaces 62, 72, and 92. With this structure as well, the operation and effects of (1) to (10) described above are also able to be obtained.

In the example embodiments described above, the variable valve timing mechanism 40 is provided with the three vanes 43A, but the number of vanes 43A is not limited to this. That is, there may be two or less or four or more vanes 43A. If there are two or less or four or more vanes 43A, one of the ambient air communication passages 81, 82, or 83 simply need be provided in each vane 43A. Also, if there are five or more vanes 43A, the ambient air communication passages 81, 82, and 83 may be provided substantially evenly in the circumferential direction of the second rotating body 43. With this structure as well, the operation and effects of (1) to (10) described above are also able to be obtained.

In the example embodiments described above, the lock mechanism for restricting the valve timing to the intermediate angle, i.e., the first lock mechanism 60 and the second lock mechanism 70, also serves to open the advance chambers 46 and the retard chambers 47 to ambient air, but the mechanism that opens the hydraulic pressure chambers 46 and 47 to ambient air is not limited to this. For example, one of the first lock mechanism 60 or the second lock mechanism 70 may be omitted. In this case, the opening mechanism 90 may be provided on the remaining vane 43A. With this structure as well, the operation and effects of (1) to (5) and (9) described above are also able to be obtained.

In the example embodiments described above, when the lock pins 61 and 71 are activated by the hydraulic pressure in the release chambers 62A and 72A, the advance chamber 46 and the retard chamber 47 that are positioned on both sides of the vane 43A with the first lock pin 61 can be opened to ambient air or closed off from ambient air, but the structure that enables the advance chamber 46 and the retard chamber 47 to be open to ambient air or closed off from ambient air is not limited to this. That is, alternatively, one of the lock pins 61 or 71 may be a restricting pin for restricting the valve timing from changing to the retard side or advance side of the intermediate angle. With this structure as well, the operation and effects of (1) to (10) described above are also able to be obtained.

In the example embodiments described above, the structures of the lock mechanisms 60 and 70 are such that the lock pins 61 and 71, the release chambers 62A and 72A, and the springs 63 and 73 are provided on the second rotating body 43, and the lock holes 64 and 74 and the lock grooves 65 and 75 are provided in the first rotating body 41. However, the structures of the lock mechanisms 60 and 70 are not limited to this. For example, the lock pins 61 and 71, the release chambers 62A and 72A, and the springs 63 and 73 may be provided on the first rotating body 41, and the lock holes 64 and 74 and the lock grooves 65 and 75 may be provided in the second rotating body 43. In this case, the first and second ambient air communication passages 81 and 82 simply need be provided in the first rotating body 41. With this structure as well, the operation and effects of (1) to (10) described above are also able to be obtained.

The lock mechanisms 60 and 70 and the opening mechanism 90 in the example embodiments described above are structured such that the pins 61, 71, and 91 provided on the second rotating body 43 are displaced toward the first rotating body 41 side by the urging force of the springs 63, 73, and 93, but this structure may also be modified as follows. That is, the pins 61, 71, and 91 may be provided in the radial direction in the first rotating body 41, and may be displaced toward the second rotating body 43 side by the urging force of the springs 63, 73, and 93. With this structure as well, the operation and effects of (1) to (10) described above are also able to be obtained.

In the example embodiments described above, an engine-driven oil pump is used as the oil pump 102, but an electric pump that is driven by an electric motor may also be used. With this structure as well, the operation and effects of (1) to (8) described above are also able to be obtained.

In the example embodiments described above, the variable valve timing mechanism 40 includes the first and second lock mechanisms 60 and 70 that fix the valve timing at an intermediate angle. However, the valve timing that is fixed by the lock mechanisms 60 and 70 is not limited to being an intermediate angle. That is, it may also be changed to the most advanced angle. In other words, any valve timing except for the most retarded angle may be used as the specific angle of the valve timing fixed by the lock mechanisms 60 and 70.

The structure of the variable valve timing apparatus to which the invention is applied, starting with the structure of the variable valve timing mechanism 40, is not limited to the structures described in the foregoing example embodiments. That is, as long as the structure includes a variable valve timing mechanism that changes the valve timing, the invention is not limited to being applied to a variable valve timing apparatus of an intake valve, but may also be applied to a variable valve timing apparatus of an exhaust valve or both an intake valve and an exhaust valve. In this case as well, operation and effects similar to the operation and effects of the foregoing example embodiments are able to be obtained.

The structure of the invention is summarized below.

A first aspect of the invention relates to a variable valve timing apparatus for an internal combustion engine. This apparatus includes a variable valve timing mechanism that changes a valve timing of at least one of an intake valve or an exhaust valve by changing a relative rotation phase of a camshaft with respect to a crankshaft; and a lock mechanism that fixes the valve timing at an intermediate angle between a most advanced angle and a most retarded angle. The variable valve timing mechanism includes i) a first rotating body and a second rotating body that are rotating bodies that rotate about the same rotational axis, the first rotating body being drivingly connected to the crankshaft and having a plurality of housing chambers surrounding the rotational axis, and the second rotating body being drivingly connected to the camshaft and having a plurality of vanes that extend in a radial direction of the rotational axis and are arranged in the housing chambers, one vane being housed in each housing chamber; ii) an advance chamber formed on one side of the vane in each housing chamber and a retard chamber formed on the other side of the vane in each housing chamber, the advance chambers and the retard chambers serving as hydraulic pressure chambers into which hydraulic fluid is supplied from an oil pump; iii) a discharge passage that extends from each of the hydraulic pressure chambers on the rotational axis side and discharges hydraulic fluid from the hydraulic pressure chambers; and iv) an opening mechanism that communicates the hydraulic pressure chambers with an ambient air space to open the hydraulic pressure chambers to ambient air at least when the first rotating body and the second rotating body have stopped rotating. The opening mechanism places at least one of the hydraulic pressure chambers that is communicated with the discharge passage in a position vertically higher than the rotational axis when the first rotating body and the second rotating body have stopped rotating at a given phase, and from which hydraulic fluid is discharged into the discharge passage, in a state constantly open to ambient air regardless of the phase at which the first rotating body and the second rotating body have stopped.

In the apparatus described above, the hydraulic pressure chambers that the opening mechanism opens to ambient air may be the retard chambers.

If the engine stops without the valve timing being fixed, the fluctuation of earn torque acting on the camshaft often times results in the rotation phase of the second rotation body ending up becoming the most retarded phase or close to the most retarded phase, so the valve timing becomes the most retarded or close to the most retarded. That is, the amount of hydraulic fluid remaining in the retard chamber will become greater than the amount of hydraulic fluid remaining in the advance chamber. Therefore, when the valve timing is fixed at the intermediate angle by pivoting the second rotating body which is accomplished by the vane rocking, the hydraulic fluid remaining in the retard chamber is more likely to be a major impeding factor than the hydraulic fluid remaining in the advance chamber. Regarding this, the invention makes it possible to more quickly fix the valve timing at the intermediate angle when the engine is started because at least this retard chamber is open to ambient air via the opening mechanism.

In the apparatus described above, the hydraulic pressure chambers that the opening mechanism opens to ambient air may be the advance chambers.

Also, as described above, when the engine is stopped without the valve timing being fixed by the lock mechanism, the hydraulic fluid remaining in the retard chamber becomes a major factor that impedes the vanes from rocking when the engine is started the next time. On the other hand, because there is no hydraulic fluid remaining in the advance chamber or, if there is hydraulic fluid remaining in the advance chamber, the amount of it is comparatively smaller than the amount remaining in the retard chamber, the hydraulic fluid remaining in the advance chamber will have little effect on the rocking of the vane. However, when the vane rocks to the advance chamber side, negative pressure is generated in the advance chamber, and the force from this negative pressure restricts the rocking of the vane. Regarding this, according to the invention, at least this advance chamber is open to ambient air via the opening mechanism, so when the engine is started, the advance chamber can be maintained at substantially atmospheric pressure, which inhibits the rocking of the vane from being restricted by the effect of the negative pressure generated in the advance chamber, and as a result, the valve timing is able to be quickly fixed at the intermediate angle by the lock mechanism.

In the apparatus described above, the hydraulic pressure chambers that the opening mechanism opens to ambient air may be the retard chamber positioned on one side of a specific vane and the advance chamber positioned on the other side of the specific vane.

According to the invention, both the retard chamber and the advance chamber inside one concave portion that is divided by a specific vane are open to ambient air. Therefore, the hydraulic fluid remaining in the retard chamber can be quickly discharged via the discharge passage, while the pressure inside the advance passage can be maintained at substantially atmospheric pressure, which enables the generation of negative pressure generated when the vane rocks to be suppressed. As a result, the air pressure and the hydraulic pressure in the hydraulic pressure chambers make it possible to suitably inhibit the rocking of the vane from being restricted. As a result, the amount that the second rotating body pivots can be increased, so the valve timing can be quickly fixed at the intermediate angle.

Incidentally, the opening mechanism may include an ambient air communication passage that communicates the hydraulic pressure chambers with the ambient air space, and an on-off valve that is provided in the ambient air communication passage and selectively opens and closes the ambient air communication passage. Also, the opening mechanism may displace a valve body of the on-off valve to a position that closes the ambient air communication passage while the engine is operating, and displace the valve body to a position that opens the ambient air communication passage when the engine is stopped.

Also, an electromagnetic valve or the like may also be employed as the on-off valve provided in the opening mechanism, for example. The on-off valve may include the valve body that is displaced to the position that closes the ambient air communication passage based on hydraulic pressure of hydraulic fluid supplied from the oil pump while the engine is operating, and that is displaced to the position that opens the ambient air communication passage based on the supply of hydraulic fluid from the oil pump being stopped when the engine is stopped. According to this structure, there is no need to separately provide a driving source for displacing the valve body, so the structure of the opening mechanism can be simplified.

The variable valve timing apparatus described above may also include a flow control valve that switches the state of the lock mechanism between a locked state and an unlocked state by controlling a supply/discharge state of hydraulic fluid with respect to the lock mechanism. Also, the opening mechanism may switch a communication state between the hydraulic pressure chambers and the ambient air space based on hydraulic pressure of hydraulic fluid that is directly circulated from the oil pump, regardless of a control state of the flow control valve. For example, when the valve timing is fixed to the intermediate angle by activating the lock mechanism to restrict the relative rotation of both the rotating bodies while the engine is operating, such as while the engine is idling, hydraulic fluid is supplied from the oil pump to the opening mechanism, such that communication between the hydraulic pressure chambers and the ambient air space is closed off by the valve body. Therefore, even if the lock mechanism is in a locked state while the engine is operating, with the opening mechanism, hydraulic fluid in these hydraulic pressure chambers will not be discharged through the discharge passages. Instead, these hydraulic pressure chambers are maintained tightly closed (i.e., oil tight). As a result, relative rotation of both the rotating bodies is also restricted by the hydraulic pressure in these hydraulic pressure chambers, in addition to the lock mechanism, so the valve timing can be more reliably fixed at the intermediate angle.

The variable valve timing apparatus described above may also include a flow control valve that switches the state of the lock mechanism between a locked state and an unlocked state by controlling a supply/discharge state of hydraulic fluid with respect to the lock mechanism. Also, the opening mechanism may control the supply and discharge of hydraulic fluid via the flow control valve.

According to the invention, the hydraulic pressure chamber is able to be selectively communicated with and closed off from the ambient air space by controlling the supply and discharge of hydraulic pressure with the flow control valve. Also, in the variable valve timing apparatus described above, the on-off valve may include the valve body that is displaced to the position that closes the ambient air communication passage by centrifugal force generated as the first rotating body and the second rotating body rotate while the engine is operating, and that is displaced to the position that opens the ambient air communication passage by urging force of a spring when the first rotating body and the second rotating body have stopped rotating when the engine has stopped.

As described above, an electromagnetic valve or the like may also be employed as the on-off valve provided in the opening mechanism, for example. However, it is preferable to employ a structure in which the on-off valve includes the valve body that is displaced to the position that closes the ambient air communication passage by centrifugal force generated as the first rotating body and the second rotating body rotate while the engine is operating, and that is displaced to the position that opens the ambient air communication passage by urging force of a spring when the first rotating body and the second rotating body have stopped rotating when the engine has stopped, as described above. According to this structure, there is no need to separately provide a driving source for displacing the valve body, so the structure of the opening mechanism can be simplified.

While the invention has been described with reference to example embodiments thereof, it is to be understood that the invention is not limited to the described embodiments or constructions. The invention is intended to cover various modifications and equivalent arrangements. In addition, while the various elements of the disclosed invention are shown in various example combinations and configurations, other combinations and configurations, including more, less or only a single element, are also within the scope of the appended claims. 

1. A variable valve timing apparatus for an internal combustion engine, comprising: a variable valve timing mechanism that changes a valve timing of at least one of an intake valve or an exhaust valve by changing a relative rotation phase of a camshaft with respect to a crankshaft; and a lock mechanism that fixes the valve timing at an intermediate angle between a most advanced angle and a most retarded angle, wherein the variable valve timing mechanism includes i) a first rotating body and a second rotating body that are rotating bodies that rotate about the same rotational axis, the first rotating body being drivingly connected to the crankshaft and having a plurality of housing chambers surrounding the rotational axis, and the second rotating body being drivingly connected to the camshaft and having a plurality of vanes that extend in a radial direction of the rotational axis and are arranged in the housing chambers, one vane being housed in each housing chamber; ii) an advance chamber formed on one side of the vane in each housing chamber and a retard chamber formed on the other side of the vane in each housing chamber, the advance chambers and the retard chambers serving as hydraulic pressure chambers into which hydraulic fluid is supplied from an oil pump; iii) a discharge passage that extends from each of the hydraulic pressure chambers on the rotational axis side and discharges hydraulic fluid from the hydraulic pressure chambers; and iv) an opening mechanism that communicates the hydraulic pressure chambers with an ambient air space to open the hydraulic pressure chambers to ambient air at least when the first rotating body and the second rotating body have stopped rotating, and wherein the opening mechanism places at least one of the hydraulic pressure chambers that is communicated with the discharge passage in a position vertically higher than the rotational axis when the first rotating body and the second rotating body have stopped rotating at a given phase, and from which hydraulic fluid is discharged into the discharge passage, in a state constantly open to ambient air regardless of the phase at which the first rotating body and the second rotating body have stopped.
 2. The variable valve timing apparatus according to claim 1, wherein the hydraulic pressure chambers that the opening mechanism opens to ambient air are the retard chambers.
 3. The variable valve timing apparatus according to claim 1, wherein the hydraulic pressure chambers that the opening mechanism opens to ambient air are the advance chambers.
 4. The variable valve timing apparatus according to claim 1, wherein the hydraulic pressure chambers that the opening mechanism opens to ambient air are the retard chamber positioned on one side of a specific vane and the advance chamber positioned on the other side of the specific vane.
 5. The variable valve timing apparatus according to claim 1, wherein the opening mechanism includes an ambient air communication passage that communicates the hydraulic pressure chambers with the ambient air space, and an on-off valve that is provided in the ambient air communication passage and selectively opens and closes the ambient air communication passage; and the opening mechanism displaces a valve body of the on-off valve to a position that closes the ambient air communication passage while the engine is operating, and displaces the valve body to a position that opens the ambient air communication passage when the engine is stopped.
 6. The variable valve timing apparatus according to claim 5, wherein the on-off valve includes the valve body that is displaced to the position that closes the ambient air communication passage based on hydraulic pressure of hydraulic fluid supplied from the oil pump while the engine is operating, and that is displaced to the position that opens the ambient air communication passage based on the supply of hydraulic fluid from the oil pump being stopped when the engine is stopped.
 7. The variable valve timing apparatus according to claim 6, further comprising: a flow control valve that switches the state of the lock mechanism between a locked state and an unlocked state by controlling a supply/discharge state of hydraulic fluid with respect to the lock mechanism, wherein the opening mechanism switches a communication state between the hydraulic pressure chambers and the ambient air space based on hydraulic pressure of hydraulic fluid that is directly circulated from the oil pump, regardless of a control state of the flow control valve.
 8. The variable valve timing apparatus according to claim 6, further comprising: a flow control valve that switches the state of the lock mechanism between a locked state and an unlocked state by controlling a supply/discharge state of hydraulic fluid with respect to the lock mechanism, wherein the opening mechanism controls the supply and discharge of hydraulic fluid via the flow control valve.
 9. The variable valve timing apparatus according to claim 5, wherein the on-off valve includes the valve body that is displaced to the position that closes the ambient air communication passage by centrifugal force generated as the first rotating body and the second rotating body rotate while the engine is operating, and that is displaced to the position that opens the ambient air communication passage by urging force of a spring when the first rotating body and the second rotating body have stopped rotating when the engine has stopped. 